[sdiy] 4049/4069 linear mode

[Kyle Stephens]

Tom Bugs did something along the lines of what you might be doing (is it a NAND synth?), maybe get some ideas there:

http://www.bugbrand.co.uk/index.php?main_page=product_info&cPath=1_14&products_id=34

He uses a 4069 for distortion too, as does the JH Wasp clone:

http://www.jhaible.de/tonline_stuff/hj_wasp.html

I forget off the top of my head if the distortion is stock to the original Wasp or not...

JH and Ken Stone have identical schems for it, though Ken's is a little cleaner (with my apologies to JH!):

http://www.cgs.synth.net/modules/cgs49_twf.html

Good luck!


_Kyle

--- On Sun, 5/31/09, Derek Holzer <derek at umatic.nl> wrote:

> From: Derek Holzer <derek at umatic.nl>
> Subject: Re: [sdiy] 4049/4069 linear mode
> To: "Scott Nordlund" <gsn10 at hotmail.com>
> Cc: synth-diy at dropmix.xs4all.nl
> Date: Sunday, May 31, 2009, 3:33 AM
> Hi everyone and thanks for the
> feedback on this particular IC!
> 
> Scott, you mentioned biasing the input of the gate for use
> as an amplifier, but all the single supply circuits I see
> using this technique such as the Anderton "Tube Fuzz" (and I
> *think* in the Wasp filter, although I'm not sure...) do not
> bias it at all.
> 
> To be more specific, I'm using this in small battery
> powered synths based on 4093 gated square wave oscillators,
> and I'm trying to get the best use of it as both gain
> control and overdrive. Should I worry about biasing in this
> case? Would I get better performance out of it if I do?
> 
> Hadn't considered driving an LED with it, was using
> discrete transistors for that as I have a ton of 4069 rather
> than 4049.
> 
> best!
> Derek
> 
> Scott Nordlund wrote:
> > As far as I know, the 4049 can source/sink more
> current, so it's suitable for driving things like LEDs.
> > 
> > Forget looking at the schematics that use the 4049 or
> 4069, look at the datasheet (for the 4069UB, not the
> buffered 4069B, since it's got additional stages that ruin
> the fun).  An input voltage of Vdd will turn the N
> MOSFET on (Vgs = Vdd) and the P MOSFET off (Vgs = 0), thus
> giving a low output voltage.  Conversely, an input
> voltage near Vss will turn the N MOSFET off (Vgs = 0) and
> the P MOSFET on (Vgs = -Vdd), producing a high output. 
> So it works as a digital inverter.  An intermediate
> voltage will result in both MOSFETS being partially turned
> on and operating in a more or less linear region, though
> they weren't designed with this in mind.  This isn't
> always a good thing, as it can allow a rather high current
> to flow from Vdd to Vss (though these chips seem to be able
> to handle it).  If you've got it biased at 1/2 Vdd, a
> small signal superimposed on top of this will be amplified
> and inverted.  Thus it's also an amplifier, though not
> a very good one.  It uses a lot of powe
> r!
> >   and isn't particularly linear,
> especially for large input amplitudes, but sometimes this is
> what you want.  The very high input impedance is an
> added bonus.
> 
> -- ::: derek holzer ::: http://blog.myspace.com/macumbista ::: http://www.vimeo.com/macumbista :::
> ---Oblique Strategy # 125:
> "Only a part, not the whole"
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